In typical fantasy leagues, people generally don't choose defenses based on scoring touchdowns. There's some luck involved in those scores, and not a huge amount of variance. The NFL average is under 3 such touchdowns per season, so the difference between above- and below-average is small.
But the gap between the very best and very worst teams is greater than you might expect. It's been a factor in Kansas City having one of the best fantasy defenses in recent years.
Over the last five seasons, Kansas City has scored 27 touchdowns on defensive (21) and kick returns (6). That's nearly double the league average (14), and 4 more than any other team. It's not due to one big year, either; Kansas City has at least 4 touchdowns in all five of those years.
|DEFENSIVE AND KICK RETURN TDS, 2015-2019|
At the other end of the spectrum, four teams have only 6 such touchdowns. The Browns and Raiders have generally been doormats, but Green Bay and Dallas have had credible defenses and made playoff appearances. So scoring only 6 touchdowns on defense or kick return plays is pretty remarkable.
A turnaround can be quick. Note that San Francisco scored more such touchdowns last season (5) than in the previous four years combined (4). Maybe Green Bay can make a similar step up.
But it's something to factor in when choosing a defense, and a piece of why Kansas City looks like a top-5 type of fantasy group again.